Multilayer components are, inter alia, capacitors and piezo actuators, which respectively contain alternating dielectric layers and inner electrodes. In piezo actuators, the dielectric layers are furthermore piezoelectric. Piezo actuators are therefore piezo elements.
Piezo elements are used inter alia in positioning elements, ultrasound transducers, sensors and in inkjet printers, as well as in automobile technology such as driving fuel injection devices. The mode of action of a piezo element is based on deformation of piezoceramic materials, for example, lead zirconate titanate, under the effect of an electric field. When an electric voltage is applied to the piezo element, it expands in a direction perpendicular to the generated electric field (inverse piezo effect).
Advantages of piezo elements are, inter alia, their relatively high speed, relatively high efficiency and, when used as a piezo actuator, relatively short travel.
If a relatively long travel is intended to be achieved with the piezo actuator, however, then a piezo stack of a plurality of alternately successive piezoelectric layers and inner electrode layers is used for the piezo actuator, as disclosed, for example, in JP 03-174783 A.
The piezo actuator disclosed in JP 03-174783 A is configured such that the inner electrode layers electrically connect alternately to outer electrodes arranged on mutually opposite outer surfaces of the piezo stack. The inner electrode layers, which electrically connect to one of the two outer electrodes, are therefore continued as far as the outer side on which this outer electrode is arranged, for electrical connection to the outer electrode. So that the inner electrode layers are electrically insulated from the other outer electrode, however, the inner electrode layers do not reach as far as the outer side of the piezo stack, on which the further outer electrode is arranged. In these regions, the inner electrode layers are set back from the outer side. This is achieved by providing the piezo stack with silicone resin-filled slots in these regions.
Due to the set-back inner electrode layers, there are so-called “inactive zones” in piezoelectric layers assigned to these regions. Usually, the inactive zones are produced during the layer-wise production of the piezo stack. Tolerances for the processes of stacking, separation, debinding and grinding during the production of the piezo stack with inactive zones, and the requirement of reliable electrical insulation of the inner electrode layers from the corresponding outer electrode, lead to relatively large inactive zones, typically 10 percent of the piezo stack cross section. The inactive zones, through which there is a reduced electric field strength when an electric voltage is applied to the outer electrode or inner electrode layers, and which therefore expand less strongly than the other, active zones when an electric voltage is applied. This leads to mechanical stresses, particularly in the inactive zones and the edge regions joining with the inactive zones, and can lead to so-called “poling cracks” in the inactive and active zones of the piezoelectric layers, as well as in the outer electrodes. The risk of poling cracks is commensurately greater when the inactive zones are larger.
It could therefore be helpful to provide a multilayer component and a method for its production, with which the performance during operation is improved, in particular, to provide a piezo actuator with which the mechanical stresses in the piezoceramic during operation of the piezo actuator are substantially reduced.